A lens system for forming a final image of an object, said system having an object side and an image side and forming a first intermediate real image between the object and final image, said system comprising a moving lens group containing the intermediate real image as the magnification of the final image is changed. The lens system is configured as a whole system so that optical aberrations at the intermediate real image, including field curvature, focus, astigmatism, distortion and color separation, are allowed to be of substantially greater magnitude than the corresponding optical aberrations of the final image.